The present invention relates generally to medical devices and methods for using such devices. More particularly, the present invention pertains to sensors, methods of implanting sensors and systems for use of such implanted sensors in the treatment of respiratory disorders.
Sleep apnea, an airway disorder, has been known for some time as a medical syndrome in two generally recognized forms. The first is central sleep apnea, which is associated with the failure of the body to automatically generate the neuromuscular stimulation necessary to initiate and control a respiratory cycle at the proper time. Work associated with employing electrical stimulation to treat this condition is discussed in Glenn, xe2x80x9cDiaphragm Pacing: Present Statusxe2x80x9d, Pace, V.I, pp 357-370 (July-September 1978).
The second sleep apnea syndrome is known as obstructive sleep apnea. Ordinarily, the contraction of the dilator muscles of the upper airways (nose and pharynx) allows their patency at the time of inspiration. In obstructive sleep apnea, the obstruction of the airways results in a disequilibrium between the forces which tend to collapse airways (negative inspiratory transpharyngeal pressure gradient) and those which contribute to their opening (muscle contraction). The mechanisms which underlie the triggering of obstructive apnea include a reduction in the size of the superior airways, an increase in their compliance, and a reduction in the activity of the muscle dilator. The muscle dilators are intimately linked to the respiratory muscles and these muscles respond in a similar manner to a stimulation or a depression of the respiratory center. The ventilatory fluctuations observed during sleep (alternately hyper and hypo ventilation of periodic respiration) thus favors an instability of the superior airways and the occurrence of oropharyngeal obstruction. In sleep apnea the respiratory activation of the genioglossus muscle has been particularly noted to be ineffective during sleep. The cardiovascular consequences of apnea include disorders of cardiac rhythm (bradycardia, auriculoventricular block, ventricular extrasystoles) and hemodynamic (pulmonary and systemic hypertension). This results in a stimulatory metabolic and mechanical effect on the autonomic nervous system. The syndrome is therefore associated with an increased morbidity (the consequence of diurnal hypersomnolence and cardiovascular complications).
A method for treatment of sleep-apnea syndrome is to generate electrical signals to stimulate those nerves which activate the patient""s upper airway muscles in order to maintain upper airway patency. For example, in U.S. Pat. No. 4,830,008 to Meer, inspiratory effort is monitored and electrical signals are directed to upper airway muscles in response to the monitored inspiratory effort. Or, for example, in U.S. Pat. No. 5,123,425 to Shannon, Jr. et al., a collar contains a sensor to monitor respiratory functioning to detect an apnea episode and an electronics module which generates electrical bursts to electrodes located on the collar. The electrical bursts are transferred transcutaneously from the electrodes to the nerves innervating the upper airway muscles. Or, for example, in U.S. Pat. No. 5,174,287 issued to Kallok, sensors monitor the electrical activity associated with contractions of the diaphragm and also the pressure within the thorax and the upper airway. Whenever electrical activity of the diaphragm suggests that an inspiration cycle is in progress and the pressure sensors show an abnormal pressure differential across the airway, the presence of sleep apnea is assumed and electrical stimulation is applied to the musculature of the upper airway. Or, for example, in U.S. Pat. No. 5,178,156 issued to Wataru et al., respiration sensing includes sensors for sensing breathing through left and right nostrils and through the mouth which identifies an apnea event and thereby triggers electrical stimulation of genioglossus muscle. Or, for example, in U.S. Pat. No. 5,190.053 issued to Meer, an intra-oral, sublingual electrode is used for the electrical stimulation of the genioglossus muscle to maintain the patency of an upper airway. Or, for example, in U.S. Pat. No. 5,211,173 issued to Kallok et al., sensors are used to determine the effectiveness of the stimulation of the upper airway and the amplitude and pulse width of the stimulation are modified in response to the measurements from the sensors. Or, for example, in U.S. Pat. No. 5,215,082 issued to Kallok et al., upon sensing of the onset of an apnea event, a stimulation generator provides a signal for stimulating the muscles of the upper airway at a varying intensity such that the intensity is gradually increased during the course of the stimulation. Or, for example, in U.S. Pat. No. 5,483,969 issued to Testerman et al., stimulation of an upper airway muscle is synchronized with the inspiratory phase of a patient""s respiratory cycle using a digitized respiratory effort waveform. A fully implantable stimulation system is described in Testerman et al. with a sensor implanted in a position which has pressure continuity with the intrapleural space such as the suprasternal notch, the space between the trachea and esophagus or an intercostal placement.
However, even with these modes of respiratory disorder treatment, there remain many practical difficulties for implementing them and other therapy treatments in medically useful systems. In particular, if stimulation for respiratory disorder treatment occurs in response to critical points in a respiratory effort waveform, it is important to be able to accurately detect the points at which stimulation is to be applied. To provide such accurate detection for treatment systems, the sensors utilized and the placement of such sensors must provide for an accurate and reliable respiratory effort waveform. Although various sensors and systems have been described above, there is a need in the art for additional sensors, sensor implant methods and systems for respiratory disorder treatment that provide practical and reliable respiratory effort waveforms for use in detection and treatment.
An implantable sensing device in accordance with the present invention includes a sensing element and a mounting element. The mounting element has a first end and a second end with a longitudinal axis therethrough. The sensing element is positioned at the first end of the mounting element with the mounting element having a length that is adjustable along the longitudinal axis.
In one embodiment, the sensing element is a pressure sensing element.
In another embodiment, the mounting element includes a sleeve having a first open end and a second open end with the longitudinal axis therethrough. The sensing element is positioned in the second open end and includes a lead body connected thereto extending through the second open end.
In another embodiment, the sleeve includes an outer sleeve member coupled for adjustment along the longitudinal axis with respect to an inner sleeve member. Further, the outer sleeve member may be an outer threaded sleeve member and the inner sleeve member may be an inner threaded sleeve member.
In another embodiment of the device, the mounting element further includes a flexible element about the first open end. The flexible element extends outwardly relative to the longitudinal axis.
In yet a further embodiment of the device, the mounting element includes a flange element extending outwardly relative to the longitudinal axis from at least a portion of the second end.
An implantable sensing device for implantation in a bone in accordance with the present invention is also described. The bone has an anterior surface and a posterior surface. The device is like the device described above with the flange element extending outward relative to the longitudinal axis from at least a part of the second open end for direct or indirect contact with the anterior surface of the bone and the flexible element about the first open end for direct or indirect contact with the posterior surface of the bone.
A method of implanting a sensor for sensing respiratory characteristics is also described. The method includes providing a sensing element and drilling a hole in a bone. The hole extends to the intrathoracic cavity. The sensing element is inserted into the hole and positioned in communication with a region in the intrathoracic cavity.
In one embodiment, the hole is drilled in the sternum. Preferably, the hole is drilled in the manubrium of the sternum.
Another implantable sensing device in accordance with the present invention includes a sensing element and a mounting assembly. The mounting assembly has at least one open end and a longitudinal axis therethrough. The sensing element is positioned at the first open end of the mounting element with the mounting assembly including a flexible element positioned about the first open end extending outwardly relative to the longitudinal axis.
In one embodiment of the device, the mounting assembly is adjustable along the longitudinal axis. In other embodiments of the device, the flexible element is a thin flexible material about the perimeter of the first open end extending rearwardly of the first open end and outwardly relative to the longitudinal axis, the flexible element is formed of a radio opaque material, and/or the flexible element is molded onto the first open end and is of an umbrella-like configuration.
A method for positioning an implantable sensor in accordance with the present invention is also described. The method includes providing a sensor mounting assembly having at least one open end and a longitudinal axis therethrough with a sensing element positioned therein. The mounting assembly includes a flexible element positioned about the first open end in a normal configuration extending outwardly relative to the longitudinal axis. A hole is drilled in a bone and the sensor mounting assembly is inserted into the hole such that when inserted into the hole the flexible element about the first open end collapses towards the longitudinal axis.
In one embodiment of the method, the sensor mounting assembly is removed from the hole. The flexible element collapses towards the longitudinal axis during removal.
In another embodiment of the method, the sensor mounting assembly is inserted into the hole such that when the flexible element extends beyond the hole, the flexible element reverts to its normal configuration.
A method for generating a respiratory effort signal for use in the treatment of respiratory disorders in accordance with the present invention is described. The method includes securing a sensing element at a location in close proximity to the posterior surface of the manubrium. A characteristic of respiratory effort is measured at the location and a signal representative thereof is generated.
In one embodiment of the method, the securing step includes drilling a hole through the manubrium and inserting the sensing element into the drilled hole.
In another embodiment of the method, the sensing element is positioned in a sleeve having a first open end, a second open end, a longitudinal axis therethrough, and a length adjustable along the longitudinal axis. The sensing element is positioned in the sleeve at the first open end with a lead connected thereto extending through the second open end. At least one of the first and second open end has a securing element extending therefrom with the sensor element secured in the location using the securing element.
In yet further embodiments, the securing element may be a flexible element about the first open end extending outwardly relative to the longitudinal axis, the securing element may be a flange element extending from the second open end and outwardly relative to the longitudinal axis, or both such elements may be present.
A method for providing stimulation of a patient to treat respiratory disorders in accordance with the present invention is also described. The method includes sensing a characteristic of respiratory effort at the manubrium in proximity to the brachiocephalic vein and generating a respiratory effort signal in response thereto. The respiratory effort signal is monitored to detect an event for triggering stimulation and stimulation is provided in response to the detection of the stimulation event.
In one embodiment of the method, a pressure sensing element is positioned at the manubrium and at a location in proximity to the brachiocephalic vein and pressure at the location is measured.
A system for providing stimulation of a patient to treat respiratory disorders in accordance with the present invention is also described. The system includes an implantable sensing element positioned at the manubrium of the patient and in proximity to the brachiocephalic vein for sensing a characteristic of respiratory effort. Stimulation control means receives a signal from the sensing element representative of the sensed characteristic and generates a stimulation signal in response to detection of an event for triggering stimulation. At least one electrode receives the stimulation signal.
In one embodiment of the system, a lead body is connected to the sensing element and the sensing element is positioned in a sleeve. The sleeve has a first open end and a second open end with a longitudinal axis therethrough. The sensing element is positioned in the sleeve at the first open end with the lead body extending through the second open end. The sleeve has a length that is adjustable along the longitudinal axis.
In yet further embodiments of the system, the sleeve includes a flexible element about the perimeter of the first open end extending outwardly relative to the longitudinal axis and/or the sleeve includes a flange element extending outwardly relative to the longitudinal axis from at least a part of the second open end.